Ideas Needed - Editing/Approval Process

I have a document library, in which all of our published documents reside. Everyone has read access to these documents.

In order to have a controlled editing and approval process, I was thinking of setting up a process that could be started by appropriate users. The process would move the document to a working area - a document library which stored all documents which are currently being worked on by users.

So basically I would have 2 document libraries:
Published Documents - this is the latest published version of each document, which everyone has read access to
Working Documents - this stores documents which people are working on at the moment. Once they have finished working on the document, they could start an approval workflow which get the document signed off, and then move the document back to the "Published Documents" library

I was intending to achieve this by creating a K2 Sharepoint Workflow (using K2 Sharepoint Workflow Integration), so that the user can drop down the menu on an item, and then choose "Workflows", and then start the "Edit Document" workflow.

Unfortunately, I have found that in order for someone to start a Sharepoint workflow on a document in a document library, they require edit permissions on the document.

Does anyone have any ideas on how I could approach this to enable anyone who can read the document to start the edit process, without giving them Edit permissions in the "Published Documents" document library??

I am happy to consider any alternative that will get the job done - I am not fussed on whether it uses Sharepoint Workflow Integration, or is fired by an event occurring...

Thanks in advance for any assistance.